procedure

Melt butter in heavy large saucepan over medium heat. Add celery and onion. Cover and cook until very tender, stirring occasionally, about 20 minutes. Stir in celery root, potato, garlic and celery salt. Add 2 cans broth; cover and simmer until all vegetables are very tender, about 30 minutes. Purée half of soup in blender and add back add the cream and heat. Season with salt and pepper.